1. Technical Field of the Invention
The present invention relates to a fan consisting of a fan wheel driven by an electromotor, whereby the electromotor is controlled in relation to its rotational speed by a control unit.
2. Discussion
An open-loop control system for an electromotor for a fan, that delivers a constant back-pressure, is known from U.S. Pat. No. 5,019,757. A required speed is determined from the motor torque, speed signal, and a preset streaming pressure of the fan, and is achieved by means of a control algorithm.
An open-loop control system for an electromotor for a fan, that delivers a constant volume flow, is known from U.S. Pat. No. 4,978,896. A required speed is determined from the motor torque, speed signal, and a preset volume flow, and is achieved by means of a control algorithm.
An open-loop control system for an electromotor for a fan, that delivers a constant volume flow, is known from U.S. Pat. No. 4,806,833, whereby a required speed is determined on the basis of the speed and a preset volume flow and speed by means of a control algorithm.
A fan consists of a blower wheel, which is driven by an electromotor with a rotational speed n. The fan has the task of delivering a medium with a density xcfx81 with a volume flow {dot over (V)} against a back-pressure p. The variables p, {dot over (V)}, n and other electrical variables of the motor are measured on a metering pipe. The description of the back-pressure across the volume flow is represented in a so-called air performance characteristic p=f({dot over (V)}), see FIG. 1. In conventional fans without speed control, the blower wheel will arrive at a speed in which the motor output torque equals the fan""s input torque. The air performance characteristics shown in FIG. 1 were each recorded for a particular speed. If different rotational speeds are taken as a basis, then a particular curve can be measured for each speed, so that a whole field of characteristic curves can be produced for a special fan. But these kinds of fields can also be produced for different wheel sizes and/or different densities of the medium to be delivered.
In a fan with a so-called xe2x80x9cartificialxe2x80x9d characteristic curve, the fan is supposed to achieve a preset p({dot over (V)}) curve. Here, closed-loop control of the speed is supposed to be conducted exactly in such a way that this preset air performance characteristic is obtained. Such a control is relatively easy to realize, if the variables p and/or {dot over (V)} are measured directly at the fan. But this requires expensive measurements using expensive sensors for pressure and/or volume flow.
Proceeding from the known prior art, in which only one particular characteristic curve can be set, it is the objective of the present invention to make available a fan, which can be driven on any arbitrary artificial characteristic curve by controlling the speed by measuring the motor parameters, electrical variables, and the speed.
In accordance with the invention, this is achieved for a fan of the type described in the introduction, in that an actual-value signal corresponding to the fan""s actual speed is measured and compared with a control signal corresponding to a required speed, and the actual speed is adjusted to the required speed by means of the control unit, wherefore the actual speed na and an actual motor current ia or a supply current Ib are measured and conducted to a microcontroller as input signal variables, and the fan-specific data such as wheel diameter, density of the conveying medium, fan coefficients, motor coefficients, and a preset artificial characteristic curve p=ƒ({dot over (V)}s) are stored in the microcontroller as default values, and the microcontroller generates the required-speed signal ns, which is a function of the electrical current variables Ia or Ib and the actual speed na, based on the preset artificial characteristic curve ps=ƒ({dot over (V)}) where ps=required operating pressure and Vs=required volume flow.